The prior art machines for making filter bags, in particular with infusion products, are designed according to various architectures depending on the shape of the filter bag and/or the type of product it contains.
With particular reference to vertical axis machines, such machines comprise a feed channel extending vertically on which a continuous strip of filter paper is wrapped to form a tube, into which the product is made to fall by gravity using suitable feeding and dosing devices.
Once filled with product, the tube is intercepted, during tube feed, by a forming and closing station for forming the filter bag into the desired shape and for closing the open edges.
A problem particularly felt in this type of machine is that of guaranteeing the filling of each filter bag with the a predetermined dose of product and at the same time reducing the variability in weight of the product introduced in different filter bags.